This page in a nutshell: Wikipedia articles ought to be written in plain English. Jargon, buzzwords, tautologies and vague abstractions ought to be avoided to the greatest extent possible. Articles with puffery are also not acceptable.

The art of writing plain English has to be learned. Strunk and White's The Elements of Style and Gowers' The Complete Plain Words are two justly famous manuals that try to teach it. The guidance in manuals such as these is not universally applicable – Swinburne or Jeremy Taylor rewritten to comply with it would lose all interest – but it does apply unequivocally to Wikipedia articles.

An encyclopedia article is a piece of expository prose, and as such it has an objective purpose. This purpose is not to impress its readers with your learning or vocabulary, even if that is your subjective purpose for writing it. Instead, its purpose is to impart information, whether by introducing new knowledge to people who lack it or by reminding people of what they had half-forgotten. Plain words best serve this purpose.

Vigorous writing is concise. A sentence should contain no unnecessary words, a paragraph no unnecessary sentences, for the same reason that a drawing should have no unnecessary lines and a machine no unnecessary parts. This requires not that the writer make all his sentences short, or that he avoid all detail and treat his subjects only in outline, but that every word tell.

Ernest Gowers gave many examples of writing that could be improved. This is one from the UK Government about police complaints procedures:[1]

N

Under the arrangements described, in any case not referred to the assessor he will be able, in effect, to call it in and determine whether by reason of the gravity of the allegation or other exceptional circumstances it should be investigated under his supervision.

As Gowers says, "Here is a translation ... [which has] made the sentence far clearer, and at the same time exactly halved the number of words":

Y

Under this proposal, the assessor can call in any complaint not referred to him and decide whether he should supervise the investigation.

Jargon and technical vocabulary are inevitable in many fields. Whenever using them, explain them briefly or give a wikilink to help the reader understand the word.

For example, a legal word like estoppel may confuse a reader who is not a lawyer. Estoppel essentially means that "the law is not amused when you contradict yourself, whether by words or actions, after someone has acted on what you said before"; however, the scholastic method of the law has clouded its meaning over time. The estoppel article should clarify both these points for readers and allow them to understand the word in context.

Jargon and lack of context pose a particular problem in mathematical articles. Wikipedia has many of these articles; many could improve with editing. The difficulty here comes from framing the articles for the right audience. The professional mathematician may find a given Wikipedia article lacking in detail, while lay readers may find it baffling. Information presented from the viewpoint of the sociology of science goes a long way towards making these articles interesting and intelligible to non-mathematicians.

More context is valuable in these situations. As a writer, include some history of the problem the theorem was meant to solve or cite practical applications of the theorem. This sort of information allows a non-mathematician to retain knowledge from the mathematical article.

To call someone a terrorist is a value judgment; tell us instead that he bombed the subway and that his compatriots issued a statement containing political demands, and you are as close to neutrality as mere mortals have the power to achieve. Concrete words are inherently less pointed than any labels, and the truer path to neutrality is to replace the abstract with the concrete.

If a person within a company starts an article about that company, it may be considered a conflict of interest: advertising a company versus providing information about it. Nonetheless, the business – and its article – may still be considered notable if it provides useful information about the business.

Inappropriate vagueness and abstractions, especially the vogue words commonly described as buzzwords, are a frequent problem in articles about businesses. An informative, clear, and succinctly written article trumps one filled with buzzwords.

Ajax Waste Solutions, Inc. is a corporation that manufactures toilets and other bathroom and plumbing fixtures for public and institutional use and sells them wholesale to building contractors. . . .

Avoid using the word "solution" to describe a business's product or service offerings. The use of this word is inherently non-neutral, since it implies that the business's offerings can indeed solve a problem. It is also inherently vague, leaving the reader to guess whether the product is software, an ongoing service, or some combination of both.

Use concrete nouns to describe a business's products or services. If the business makes or sells things, an appropriate description would tell us what is inside the boxes at the warehouse or on the shelves of its shops. If the business provides services to people, the sorts of problems its representatives discuss with the customers is helpful information. If the business's product is software, the article should provide a specific description of what it does and the intended market: